Question

A cellphone store has 120 cell phones in stock. Of these, 45 have keyboards. The manager of the store wants to add more cell phones with keyboards so that 40% of the stock has keyboards.

Answer 1

Answer:

5

Step-by-step explanation:

Let x be the number of cell phones with keyboards needed.

40% = $\frac{40}{100}$

$\frac{x+45}{x+120}$ = $\frac{40}{100}$

x+45 = 40 -----1

x+120 = 100 -----2

You would want to make the total of 1 the same as 2.

1×$\frac{100}{40}$: 2.5+112.5 = 100 -----3

Now 2 and 3 are equal.

x+120 = 2.5x+112.5

Isolate the x and numbers.

120-112.5 = 2.5x-x

Simplify.

1.5x = 7.5

x = $\frac{1}{1.5}$ × 7.5

x = 5

The manager of the store needs to add 5 more cell phones with keyboards.